The present invention relates to a method for producing ranged structural products, and more particularly to a method for producing structural beams, for example, beams having H and I shapes, directly from slabs.
Since the early years of the 20th century, when rolling ranged structural products as integral elements was first accomplished, there has been a constant need to save time, energy, and cost in the production of these products. The original production methods required a cast billet to be reheated and shaped into a flanged beam blank, for example, a general H shape, by rough shaping in a breakdown mill. The resultant blank was then finished in a universal mill. This method, which is described in U.S. Pat. No. 1,034,361, Jul. 30, 1912, by Grey, required both a breakdown mill and a universal mill.
As the rolled flanged products became widely used, more specific shapes, sizes, and weights of products were specified by the construction industry. The steel industry complied and today a wide variety of different rolled flanged products are produced in rolling mills throughout the world.
It became apparent that the cost of facilities, materials, and time might be reduced if a particular rectangular shape could be sent directly to the universal mill for rolling into a finished product. It was also recognized that if the rectangular shape could be sent directly to the universal mill, the breakdown mill could be eliminated, and facility and production costs would be reduced. In other words, it became an objective to produce flanged products by starting with a simple geometric cross section, e.g., a rectangular slab of metal, and accomplishing all of the shaping in a universal mill. Such slabs could come directly from a continuous caster as well known in the art, or the rolling method could start with cold slabs provided at the universal mill site.
To save energy, it is desirable that the slab, whether cold or coming directly from the caster, be brought up to rolling temperature only once during the process, prior to its entry to the universal mill. Also, it became an objective that a given slab cross section should be proportioned to enable finish rolling a large number of different finished products sizes or shapes with a minimum number of different rolls in the universal mill. And, in addition, the rolling should be accomplished with conventional horizontal and vertical rolls to allow for quick adjustment between the different product sizes.
As is apparent from the preceding discussion that feeding slabs directly into a universal mill eliminates the need for the breakdown mill and facilitates one-reheat processing of the metal.
One method for producing blanks for wide flange products from a rectangular slab is described in U.S. Pat. No. 4,420,961, Dec. 20, 1983, by Kusaba. Kusaba shows a rectangular slab being split along each of its longitudinal side edges. The slit is gradually deepened and widened to form a blank from which an H or I shape is produced after further separation of the split material of the edges to form flanges. The patent describes several other methods wherein a slab is formed into a blank for a finished product by slitting along the edges.
And, Kusaba discloses a method that requires only one reheat step during the rolling process from slab to finished product. However, in all cases, a separate breakdown mill is required to perform the splitting and shaping prior to entry into a universal mill. The yield rate of good product is affected by the apical angle of the slitting calibers, such that production of a suitable product with high production yield is not entirely predictable for new shapes.